Reservoir Engineering
General
To drill a well, a specialized piece of equipment known as a drilling rig bores a hole through many layers of dirt and rock until it reaches the oil and gas reservoir where the oil is held. The size of the borehole differs from well to well, but is generally around 12.5 to 90 centimeters wide. To cut through this rock, the drill is pushed down by the weight of the piping above it. This piping is used to pump a thick fluid known as mud into the well. This mud assists in the drilling process by maintaining the pressure below ground in the well as well as by collecting debris created from the drilling and bringing it up to the surface. As the drill digs deeper sections of piping are attached to lengthen the well.
MATERIAL BALANCE
Material balance analysis is an interpretation method used to determine original fluids-in-place (OFIP) based on production and static pressure data. The general material balance equation relates the original oil, gas, and water in the reservoir to production volumes and current pressure conditions / fluid properties. The material balance equations considered assume tank type behaviour at any given datum depth – the reservoir is considered to have the same pressure and fluid properties at any location in the reservoir. This assumption is quite reasonable provided that quality production and static pressure measurements are obtained.
RESERVOIR MANAGEMENT
The reservoir management consists on the application, within a given fiscal and contractual frame, of well-established industrial technologies and field best practices to a hydrocarbon reservoir, in order to efficiently perform the field operations and maximize the economic return of the investments. The purpose of reservoir management is to control operations to obtain the maximum possible economic recovery from a reservoir on the basis of facts, information, and knowledge. Reservoir Management relies on the use of human, technological and financial resources to capitalize on profits from a reservoir by optimizing the hydrocarbon recovery while minimizing both the capital investments and the operating costs.
ENHANCED OIL RECOVERY
Oil production is separated into three phases: primary, secondary and tertiary, which is also known as Enhanced Oil Recovery (EOR). Primary oil recovery is limited to hydrocarbons that naturally rise to the surface, or those that use artificial lift devices, such as pump jacks. Secondary recovery employs water and gas injection, displacing the oil and driving it to the surface. According to the US Department of Energy, utilizing these two methods of production can leave up to 75% of the oil in the well. The way to further increase oil production is through the Tertiary recovery method.
RESERVOIR FORECAST
Oil production forecasting is an important means of understanding and effectively developing reservoirs. Reservoir numerical simulation is the most mature and effective method for production forecasting, but its accuracy mostly depends on high-quality history matching and accurate geological models. Oil and gas development projects need production forecasts for planning purposes and to understand the economic viability of each project. Sometimes, especially in the exploration and appraisal stages, it is necessary to develop a range of production forecasts for a project based on very limited data, often in the absence of flow information for that particular field,. One of the methods often used in this type of scenario is analog studies. well.
DECLINE CURVE
Decline curve analysis (DCA) is a graphical procedure used for analyzing declining production rates and forecasting future performance of oil and gas wells, and it has been widely used since 1945. Oil and gas production rates decline as a function of time; loss of reservoir pressure, or changing relative volumes of the produced fluids, are usually the cause. Fitting a line through the performance history and assuming this same trend will continue in future forms the basis of DCA concept. It is important to note here that in absence of stabilized production trends the technique cannot be expected to give reliable results.
RESERVOIR ESTIMATION
In the management of oil properties, it is always desirable to know the future behavior of oil wells and oil reservoirs. Some estimation of the quantity of oil and gas that will be produced must be made as a basis for decisions on possible returns on investments in lifting equipment, drilling of additional wells, and other operating expenditures. In new or wildcat areas, operating expenditures are considered highly speculative, but in the completion of partly drilled and the operation of producing fields it is good business to remove as much speculation as possible. An accurate knowledge of oil and gas reserves in such cases would solve many management problems.